1. Field of the Invention
This invention relates to an improved motor controller and more particularly to a motor controller for a D.C. series motor by which plural batteries are connected in parallel for motor acceleration, and by which after a time delay the batteries may be connected in series without opening the parallel battery connections for normal running speed.
2. Description of the Prior Art
It is broadly old in the prior art to utilize battery operated series D.C. motors to drive mining and other heavy industrial equipment. In order to prolong the life of the equipment, it is important to gradually bring the motor up to speed. One of the methods utilized in the prior art for accelerating a D.C. series motor is to provide a multiple voltage source of energy and to start the motor at a reduced voltage, then to gradually increase the voltage. A common multiple voltage source includes a plurality of batteries which may be connected variously in parallel and in series in order to place different voltages across the motor, the parallel connection of plural batteries provide a lower voltage than a series connection of the batteries. In the past, the change over from a parallel connection to a series connection has commonly involved opening the parallel battery connections and then closing the series battery connections. The following patent is illustrative of a system of the aforesaid type:
U.S. Pat. No. 3,223,908, Hutchinson et al, Dec. 14, 1965.
A disadvantage of a system which requires mechanical switching to open the parallel circuits before connecting the series circuit is that the system will have substantial current spikes with consequent injurious effect upon the equipment.
More recently an effort has been made to avoid opening the circuit between the motor and its power source when changing from a parallel battery connection to a series battery connection. The following patent discloses a motor control system by which the change over from a parallel battery connection to a series battery connection is made without first opening the parallel battery connection and then closing the series battery connection:
U.S. Pat. No. 3,264,540 Dannettell, Aug. 2, 1966
U.S. Pat. No. 3,264,540 discloses the use of uni-directional conductors to prevent short circuiting the parallel connected batteries when a circuit connecting the batteries in series is closed.